Traditionally, there has been known a portable device such as a handheld terminal and a personal digital assistant (PDA) with a radio communication function. There has been proposed a plane-shaped multiband antenna as an antenna for radio communication to be mounted on the portable device (e.g., see Patent document 1). The multiband antenna can easily be stored in a portable device owing to the plane-shape, and radio communication can be performed at a plurality of resonance frequencies with the multiband antenna.
Further, there has been known an inverted F antenna having an inverted F antenna element as an antenna for radio communication. Furthermore, a multiband inverted F antenna has been proposed as well (e.g., see Patent document 2).